Messages in this thread | | | From | David Stevens <> | Date | Mon, 13 Sep 2021 17:21:49 +0900 | Subject | Re: [PATCH v7 0/7] Fixes for dma-iommu swiotlb bounce buffers |
| |
Is there further feedback on these patches? Only patch 7 is still pending review.
-David
On Mon, Aug 30, 2021 at 2:00 PM David Stevens <stevensd@chromium.org> wrote: > > This patch set includes various fixes for dma-iommu's swiotlb bounce > buffers for untrusted devices. > > The min_align_mask issue was found when running fio on an untrusted nvme > device with bs=512. The other issues were found via code inspection, so > I don't have any specific use cases where things were not working, nor > any concrete performance numbers. > > There are two issues related to min_align_mask that this patch series > does not attempt to fix. First, it does not address the case where > min_align_mask is larger than the IOVA granule. Doing so requires > changes to IOVA allocation, and is not specific to when swiotlb bounce > buffers are used. This is not a problem in practice today, since the > only driver which uses min_align_mask is nvme, which sets it to 4096. > > The second issue this series does not address is the fact that extra > swiotlb slots adjacent to a bounce buffer can be exposed to untrusted > devices whose drivers use min_align_mask. Fixing this requires being > able to allocate padding slots at the beginning of a swiotlb allocation. > This is a rather significant change that I am not comfortable making. > Without being able to handle this, there is also little point to > clearing the padding at the start of such a buffer, since we can only > clear based on (IO_TLB_SIZE - 1) instead of iova_mask. > > v6 -> v7: > - Remove unsafe attempt to clear padding at start of swiotlb buffer > - Rewrite commit message for min_align_mask commit to better explain > the problem it's fixing > - Rebase on iommu/core > - Acknowledge unsolved issues in cover letter > > v5 -> v6: > - Remove unnecessary line break > - Remove redundant config check > > v4 -> v5: > - Fix xen build error > - Move _swiotlb refactor into its own patch > > v3 -> v4: > - Fold _swiotlb functions into _page functions > - Add patch to align swiotlb buffer to iovad granule > - Combine if checks in iommu_dma_sync_sg_* functions > > v2 -> v3: > - Add new patch to address min_align_mask bug > - Set SKIP_CPU_SYNC flag after syncing in map/unmap > - Properly call arch_sync_dma_for_cpu in iommu_dma_sync_sg_for_cpu > > v1 -> v2: > - Split fixes into dedicated patches > - Less invasive changes to fix arch_sync when mapping > - Leave dev_is_untrusted check for strict iommu > > David Stevens (7): > dma-iommu: fix sync_sg with swiotlb > dma-iommu: fix arch_sync_dma for map > dma-iommu: skip extra sync during unmap w/swiotlb > dma-iommu: fold _swiotlb helpers into callers > dma-iommu: Check CONFIG_SWIOTLB more broadly > swiotlb: support aligned swiotlb buffers > dma-iommu: account for min_align_mask w/swiotlb > > drivers/iommu/dma-iommu.c | 188 +++++++++++++++++--------------------- > drivers/xen/swiotlb-xen.c | 2 +- > include/linux/swiotlb.h | 3 +- > kernel/dma/swiotlb.c | 11 ++- > 4 files changed, 93 insertions(+), 111 deletions(-) > > -- > 2.33.0.259.gc128427fd7-goog >
| |